The present invention generally relates to the field of manufacturing silicon wafers in the microelectronics industry. More particularly, it relates to a method of removing residual wax from a silicon wafer polishing plate.
Silicon wafer polishing is one of the important steps of manufacturing silicon wafers in the microelectronics industry. In the process of polishing silicon wafers, wax is used to attach the silicon wafers to a single glass or ceramic (aluminum oxide) plate. After the wafers are attached, the plate is inserted into a polishing machine which applies pressure and rotation to the plate in an environment of liquid slurry. The combination effect of the pressure, rotation, and slurry improves the flatness and smoothness of the silicon wafers.
After the silicon wafer polishing process is completed, the polishing plate is removed from the polishing machine, and the wafers are removed from the polishing plate. The polishing plate can be reused, provided the residual wax is completely removed. If residual wax remains on the polishing plate, the surface of the polishing plate will not be flat enough to properly polish the next batch of wafers. In this regard, wafers must generally be polished to a relatively tight flatness specification, such as to within one micron. Accordingly, any residual wax on the polishing plate will create a non-flat surface which, in turn, may prevent the next batch of wafers from being polished to within tolerance.
It is therefore essential to completely remove all residual wax from the polishing plate before new wax is applied and unpolished wafers are attached to it. However, it is difficult to completely remove all residual wax from the polishing plate because wax collects in the contours of the plate, and particularly on the surface areas where the wafer perimeters contact the polishing plate.
Referring to TABLE 1, which is set forth below, the conventional method of removing residual wax from the polishing plate typically includes the following seven steps: The first step involves a single rinse of the plate with methylene chloride (CH.sub.2 Cl.sub.2). The next three steps involve consecutive submersions of the plate in a surfactant commonly known as RBS-35 (a proprietary surfactant manufactured by Pierce Chemical Co. in Rockford, Ill.). These steps are followed by three consecutive rinses of the plate in de-ionized (DI) water, all in combination with ultrasonic energy and heating. The temperature range for each bath is approximately 25.degree. C. to 70.degree. C. The time range for each bath is approximately 0.5 to 5 minutes.
TABLE 1 ______________________________________ CONVENTIONAL METHOD OF WAX REMOVAL Step Treatment Material ______________________________________ 1 Rinse CH.sub.2 Cl.sub.2 2 Submerge Surfactant (RBS-35) 3 Submerge Surfactant (RBS-35) 4 Submerge Surfactant (RBS-35) 5 Rinse DI Water 6 Rinse DI Water 7 Rinse DI Water ______________________________________
The primary disadvantage of the conventional method of removing residual wax from silicon wafer polishing plates is that it uses methylene chloride, which is environmentally hazardous, carcinogenic, and expensive to contain and dispose. It is therefore desirable to provide a new method for the effective removal of residual wax from glass or ceramic silicon wafer polishing plates which uses environmentally safe and low cost chemical materials.